The data on the 30 million Americans who have already cast an early vote seems to show that Democrats have an edge in several key states.

The president made a final frenetic dash through the swing states, racing the sun, the clock, and fatigue to deliver his final argument to voters.

The final-day blitz across Wisconsin, Iowa, and Ohio was aimed at shoring up the "mid-western firewall" which needs to hold to get him over the line of the 270 electoral college votes he needs for victory.

"When I tell you I know what real change looks like, it's because I fought for it, because I delivered it, because I've got the scars to prove it, because that's why my hair went grey," the weary-looking president told cheering supporters in Ohio.

"After all we've been together we can't give up on it now, we've got to keep on going and bring some more change to America."

Mr Romney was first out of the gate on Monday morning, addressing a rally in the biggest swing state of all - Florida - barely 10 hours after wrapping up an event the night before in Virginia.

He pledged that he would handle the economy better than Mr Obama and took aim at his opponent for blaming Republican predecessor George W Bush for the weak economy.

"I won't waste any time complaining about my predecessor. And I won't spend my time trying to pass partisan legislation rather than working to help America get back to work," he told a Fairfax, Virginia rally.

Mr Romney was holding five rallies in four states in what will be his longest day of campaigning.

After voting early in his home state of Massachusetts, he was considering a last-second visit to potential kingmaker state Ohio to try to drive turnout, aides said.

Mr Obama will return to his hometown Chicago, where he hopes to celebrate by becoming only the second Democrat since World War II to win a second term.

Mr Romney will return to where he launched his campaign 18 months ago: New Hampshire.

He has already made a surprise foray into Pennsylvania, a Democratic-leaning state that Republican strategists say is breaking his way.

"We're taking back the White House because we're going to win Pennsylvania," Mr Romney told a crowd of up to 30,000, according to US Secret Service estimates quoted by the campaign, who had gathered on a farm in frigid weather.

Mr Obama's advisers dismissed the trip as a sign of desperation from the challenger less than 48 hours from election day.

Former president Bill Clinton - the only other two-term Democrat - was headlining four rallies for Mr Obama on Monday in Pennsylvania, to counter Mr Romney's late push.

Democrats said they were confident of Mr Obama's small but steady lead in key swing states, but acknowledged that everything now depended on getting out the vote.

Florida, famous for the presidential election debacle 12 years ago which required the hand-counting of thousands of ballots, faced some new election-related problems ahead of voting day.

The state's Democratic Party filed a federal lawsuit on Sunday over long delays encountered by some voters who were unable to cast votes in southern Florida despite spending hours in line.

It's a fundamental human yearning to be a part of something bigger than one's self, and maybe that's what drove my mate Ash to die, far from home, in a bloody foreign war against Islamic State, writes C August Elliott.